1. Field of the Invention
This invention relates to improved systems for combustion of fuels and to methods for catalytic promotion of fuel combustion. In one specific aspect the present invention relates to catalytic systems for low NOx combustion. In one more specific aspect, this invention relates to low emissions combustors for gas turbine engines.
2. Brief Description of the Prior Art
Unlike gasoline engines which operate with near stoichiometric fuel-air mixtures, gas turbine engines operate with a large excess of air. Thus automotive type catalytic converters cannot be used for control of NOx emissions since such devices are ineffective in the presence of significant amounts of oxygen. Although selective ammonia denox systems are available, both operating and capital costs are high and energy losses significant. Moreover, such systems are much too large for any but stationary applications.
Consequently, most effort on control of gas turbine emissions has focused on development of low emissions combustors. However, despite much effort resulting in significant improvements, achievement of acceptable emissions levels does not appear feasible using the best conventional combustion systems. The catalytic combustion systems of my U.S. Pat. No. 3,928,961 yield the low required emissions levels. However, because of present materials limitations and the resulting low turndown ratios, few applications have resulted. For gas turbine combustors the requirement is not just low emissions but operability over a wide range of operating conditions. Thus, although emissions can be controlled by use of the catalytic combustors of my prior patent, the current narrow operating temperatures of such combustors, typically limited at present to temperatures between about 1400 and 1700 Kelvin, coupled with the limited durability of available catalysts for methane combustion, has severely limited applications.
The present invention overcomes the limitations of prior art systems and meets the need for reduced emissions from gas turbines and other combustion devices.